Favourable growing conditions so far this season have boosted prospects for the 2019 potato crop, as Farmers Guardian discovers in the second of our series following three agronomists from Hutchinsons through the season.
Cheshire: Andy Goulding
Principal crops: Processing varieties for crisps and chipping
A “fantastic” growing season so far means Andy Goulding has high hopes for the 2019 crop, which has established well and looks promising.
Protecting that yield potential over coming weeks is essential, especially if conditions remain conducive to blight, he says. “We’ve already had reports of blight in crops grown under fleece and last month’s rain increased the risk, so we have to monitor crops and keep spray intervals tight.”
He too favoured the oxathiapiprolin-based fungicide Zorvec earlier in June to protect crops through to the end of the rapid canopy expansion phase. On more stable canopies he recommends products based on mancozeb and zoxamide.
Any crops that are still growing will require systemic activity, such as products based on fluopicolide + propamocarb hydrochloride, while cyazofamid is better positioned towards the end of the season, he advises.
Looking ahead to desiccation, Mr Goulding acknowledges many growers will have sufficient stocks of diquat for this season, but he also recommends trying alternative strategies (chemical and flailing) on different canopies and varieties in preparation for life after final cut-off for using diquat (February 2020).
“With most processing crops, the aim is to keep building dry matter, so we want canopies to be senescing naturally before we start desiccation. I’d be happy to flail crops that are already on the way out, but you don’t want to start flailing a big, green canopy with lots of life left in it. This sudden loss of canopy can cause physiological shock which increases the risk of vascular browning.”
In such cases, he favours starting desiccation more gradually with 1 litre/ha of carfentrazone-ethyl then flail once canopies begin to die back.
“It’s important to lift crops as soon as the skin is set to minimise the risk of storage diseases developing,” he adds.
Mr Goulding also reports high levels of aphid activity, requiring vigilant and treatment where necessary. “Aphids pose greatest risk to seed crops, but they can still damage ware crops through direct feeding or virus infection in certain varieties.”
Cornwall: David Harris
Principal crops: First earlies (including under plastic), early salad varieties, crisping and traditional maincrop for local chip shops
Early crops in the south west have performed reasonably well, while demand has remained strong for contracted supplies, David Harris says.
“Crisping crops are now moving off farm, which will help growers clear ground in good time for following brassica crops. It’s nice crops are running on time for a change.”
Foliar feeding through the dry spring combined with heavy rainfall during last month kept maincrop potatoes looking well, with good yield potential, he adds.
However, some scab is starting to appear in salad crops and odd aphids are being found, with seed crops being treated. Blight pressure has also increased, requiring a switch from cymoxanil and mancozeb-type products to stronger chemistry, such as products based on oxathiapiprolin, fluopicolide + propamocarb, benthiavalicarb isopropyl + mancozeb, or mandipropamid.
“We’ll continue to modify blight programmes according to risk and conditions and alternate fungicides through the remainder of the growing season.”
Development of fluazinam-resistant blight strains means a change to strategies later in the season, as fluazinam has traditionally been the mainstay for tuber blight control, particularly in crops destined for storage, he continues.
Mr Harris plans to retain some fluopicolide + propamocarb hydrochloride and cyazofamid for use towards the end of the season.
Carfentrazone-ethyl and pyraflufen-ethyl are the two main alternatives to diquat and should both do a good job if used correctly, he adds. “Most growers will have sufficient diquat, but we will try the alternatives to make sure we know how to get the best from them.”
While carfentrazone incorporates a wetter, pyraflufen-ethyl does not, so requires a separate addition, he notes.
Mr Harris says topping is already fairly widely used in the region to reduce material going through harvesters, but acknowledges mechanical topping and spraying are slower than one pass with diquat.
Topping could also potentially increase the risk of spreading foliar problems, he warns.
Fife and Angus: Keith Brand
Principal crops: Ware (Fife area), seed (Angus)
Since the first red blight warning in early June, a robust fungicide programme and tight spray intervals have been required from the outset, says Keith Brand.
“Blight programmes are generally starting a lot earlier than we used to, and this year a lot of growers went straight in with the more powerful chemistry at seven-day intervals because the risk was so high.
“It’s almost the complete opposite to last year when dry conditions allowed many growers to extend spray intervals.
“But, after 100mm of rain in May and another 100mm-plus in June, everything looks verdant green and yield expectations are far greater than last year, at the moment.”
Mr Brand plans to alternate the stronger chemistry and maintain tight spray intervals so long as blight risk remains high, although may switch to other chemistry or less frequent applications if risk declines.
The loss of the flonicamid-based aphicide Teppeki has been a particular issue for those growing seed crops, as there are relatively few alternatives, Mr Brand says. Spirotetramat is one option, although cannot be applied until flowering.
“Fortunately we’ve not seen too many aphids in potato crops recently, but they are present in cereals, so the risk is there. Recently we have started seeing some more Myzus being trapped, especially further north, and are also seeing aphids appearing in other crops.”
Looking ahead, Mr Brand also prefers to bring cyazofamid back into the programme for late-season blight control.
He does not expect much change to desiccation plans this year given the stocks of diquat on-farm, but is wary of options in seed crops for future seasons. Flailing is generally not an option in seed potatoes due to the increased risk of black leg, so growers will have to consider other chemistry such as carfentrazone- based products.
He hopes a new product based on pelargonium oil will get approval for use, as trials indicate it could deliver good burn down of foliage.
For more information on the discoveries made by Farmacy agronomist John Chamberlain (East Anglia) click here.